Shaped hollow fabrics have many uses, but the present specification will deal primarily with those fabrics useful in the energy, telecommunications, electronics, pipeline and related industries. For example, substrates of complex shape may require interconnection, mechanical fixing, environmental protection or electrical screening etc. In each of those examples some form of encapsulation of the substrate may be required and a correspondence in size and shape between the substrate and its covering will be desirable. Hence the reason for the shaping and the hollow configuration. We have found that shaped fabrics are for some uses preferable over moulded parts due to their excellent creep performance, high strength and abrasion resistance and lack of tendency to split once cut or scored, and due to the in-line manufacturing techniques available for their production.
Hitherto hollow articles for encapsulation in the fields with which we are primarily concerned have almost always consisted of moulded material, although knitting has of course been used to make shaped articles such as gloves. For example articles such as boots (an article for encapsulation having generally about two outlets arranged at an angle to one one another), end caps, transitions and udders (an article for encapsulation having generally three or more outlets towards one end thereof) have been made from plastics materials by injection, compression or transfer moulding. These articles may be used to seal joints between cables or between pipes and to seal terminations of cables etc.
The fact that such hollow articles are preferably designed with a specific substrate in mind means that an excellent seal can be achieved resulting in good performance. The disadvantage, however, is that they are expensive to produce, especially in small quantities, because a mould has to be made for each design. Also, it may be desirable to provide an internal coating of an adhesive (for environmental sealing) or a metal (for electromagnetic screening) within the hollow article, and such coating may be extremely difficult to carry out accurately.